AB314. SPR-41 Localization of neuromuscular nicotinic receptors in the functionally reinnervated canine bladder after prolonged decentralization

Objective: We previously found that intravenous succinylcholine, a depolarizing neuromuscular nicotinic receptors blocker, prevents bladder contractions induced by new neuronal pathways established by nerve transfer in decentralized dogs. We studied the detrusor pressure response in vivo and contractile response of bladder smooth muscle strips in vitro from sham, decentralized and reinnervated animals to localize the neuromuscular nicotinic receptors involved.

Methods: Three groups of female mongrel hound dogs were used: sham (N=4), 12-month decentralized (N=3) and 6-month reinnervated (N=3). Decentralization was created by bilateral transection of all spinal roots caudal to L7, including the dorsal roots of L7 and the hypogastric nerves. Reinnervation was created by bilateral transfer of the obturator nerve to anterior vesical branches of the pelvic nerve. Two-way ANOVAs and Sidak post-hoc tests were used to determine group differences.

Results: In reinnervated dogs, blockade of neuromuscular nicotinic receptor with intravenous injections of the competitive antagonist atracurium besylate significantly reduced the increase in detrusor pressure induced by electrical stimulation of the transferred obturator nerve (L1 or L2). Atracurium did not block the increase in pressure induced by stimulation of sacral nerve roots in sham-operated controls. In vitro, neither the competitive neuromuscular nicotinic receptor antagonist d-tubocurarine nor the ganglionic antagonist hexamethonium inhibited electric field stimulation (EFS)-induced contractions of reinnervated or sham-operated control bladder strips. No contractile response was elicited in the presence of 1 µM tetrodotoxin (TTX) across groups. Similarly, EFS-evoked contractions were strongly reduced by 10 µM alpha, beta-methylene ATP (α,β-mATP) and 1 µM atropine in all groups relative to the vehicle (water).

Conclusions: In vivo blockade of nerve-evoked bladder pressure by atracurium in the reinnervated, but not sham operated controls, suggests that neuromuscular nicotinic receptors become involved in bladder contractions induced by the new neuronal pathway. Because d-tubocurarine did not block in vitro contractions induced by EFS in the reinnervated bladders, the neuromuscular nicotinic receptors involved in the new neuronal pathway must not be located in the bladder muscle or intramural ganglia and therefore, are likely in preganglionic neurons. TTX blockade validates that EFS-induced contractions at all frequencies were nerve-evoked. Both muscarinic and purinergic components contributed similarly to neurotransmission based on response to blockade of nerve evoked muscle strip contractions with a combination of atropine and α,β-mATP.

Funding Source(s): NIH-NINDS NS070267

Keywords: Neural plasticity; innervation; bladder; in vitro contractility; dog